1. Field of the Invention
This invention relates to a method for recovering multilayer plastics. More particularly, the multilayer plastics to which this invention can be applied, consists of, for example, a first layer of nylon or the saponified product of ethylene-vinyl acetate copolymer and a second layer of polyethylene or polypropylene or those containing extender pigments and/or reformed resins. The multilayer plastics are heated to 80.degree. to 200.degree. C. according to their component resins and immediately after that the heated material is peeled and crushed into the respective layer component resins by shearing force, impact force and tearing force. The crushed materials are then separated into two groups, one floats on water and the other sinks in water by the difference in their specific gravity, or separated by air current with the difference in their bulk densities which comes from the difference in their sizes and shapes, or the crushed products are recovered as the component resins by separately attracting to a positive electrode or a negative electrode with utilizing the difference in their dielectric constants or their electric resistances.
2. Description of the Prior Art
In the conventional art, single component plastic articles are often crushed into small pieces and they are used again by being heated, melted and extruded into certain shapes by extruders or the like, and the recovered products are used for several purposes.
In recent years, the technique of multilayer plastic formation has been developed in which the products such as bottles are made of multilayer materials consisting of different resins. With the development of this technique, it has become necessary to separate and reclaim the multilayer component resins.
Even when the multilayer plastics are crushed in like manner as the crushing of single component articles, since the plastic layers are bonded tightly, the multilayer plastics are only crushed into small pieces with their multilayer structure so that only the mixture of resin materials can be obtained, and only the articles made of the mixture of resins can be produced by the use of such a crushed material. The interlayer adhesive strength of a multilayer product is generally large to a considerable degree and when the multilayer products of the first layer of polyamide or the saponified ethylene-vinyl acetate resin and the second layer of polyethylene or polypropylene, are crushed at an ambient temperature, both the layers are simultaneously crushed in the laminated state since the tensile strengths of them are not so large. Accordingly, when such a crushed material is used in the reclaiming, the temperature of melting resin material must be raised to the point which is 20.degree. to 30.degree. C. higher than the high melting points of polyamide or saponified ethylene-vinyl acetate resin. Further, the recovered resin is defective in its transparency, surface property, antistress property and adhesive property. Therefore, it is necessary to eliminate such undesirable properties by using or mixing several percents of the recovered material into a fresh material. Further, the workability in molding is lowered and the production cycle becomes long. Accordingly, the most part of the crushed material has to be discarded. If the laminated material can be separated into its component materials, the whole of them can be reused which is quite advantageous in industrial view point. However, the complicated and expensive separation method must be avoided.